Hybrid oligonucleotide phosphorothioates

ABSTRACT

The invention provides hybrid oligonucleotides having phosphorothioate or phosphorodithioate internucleotide linkages, and both deoxyribonucleosides and ribonueleosides or 2&#39;-substituted ribonucleosides. Such hybrid oligonucleotides have superior properties of duplex formation with RNA, nuclease resistance, and RNase H activation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to synthetic oligonucleotides that are useful for studies of gene expression and in the antisense oligonucleotide therapeutic approach. More particularly, the invention relates to synthetic oligonucleotides that have improved qualities for such applications resulting from modifications in the sugar phosphate backbone of the oligonucleotides.

2. Summary of the Related Art

The potential for the development of an antisense oligonucleotide therapeutic approach was first suggested in three articles published in 1977 and 1978. Paterson et al., Proc. Natl. Acad. Sci. U.S.A. 74: 4370-4374 (1977) discloses that cell-free translation of mRNA can be inhibited by the binding of an oligonucleotide complementary to the mRNA. Zamecnik and Stephenson, Proc. Natl. Acad. Sci. U.S.A. 75: 280-284 and 285-288 (1978) discloses that a 13-mer synthetic oligonucleotide that is complementary to a part of the Rous sarcoma virus (RSV) genome inhibits RSV replication in infected chicken fibroblasts and inhibits RSV-mediated transformation of primary chick fibroblasts into malignant sarcoma cells.

These early indications that synthetic oligonucleotides can be used to inhibit virus propagation and neoplasia have been followed by the use of synthetic oligonucleotides to inhibit a wide variety of viruses. Goodchild et al., U.S. Pat. No. 4,806,463 (the teachings of which are hereby incorporated by reference) discloses inhibition of human immunodeficiency virus (HIV) by synthetic oligodeoxynucleotides complementary to various regions of the HIV genome. Leiter et al., Proc. Natl. Acad. Sci. U.S.A. 87: 3430-3434 (1990) discloses inhibition of influenza virus by synthetic oligonucleotides. Agris et al., Biochemistry 25: 6268-6275 (1986) discloses the use of synthetic oligonucleotides to inhibit vesicular stomatitis virus (VSV). Gao et al., Antimicrob. Agents Chem. 34:808-812 (1990) discloses inhibition of herpes simplex virus by synthetic oligonucleotides. Birg et al., Nucleic Acids Res. 18: 2901-2908 (1990) discloses inhibition of simian virus (SV40) by synthetic oligonucleotides. Storey et al., Nucleic Acids Res. 19: 4109-4114 (1991) discloses inhibition of human papilloma virus (HPV) by synthetic oligonucleotides. The use of synthetic oligonucleotides and their analogs as antiviral agents has recently been extensively reviewed by Agrawal, Trends in Biotech 10: 152-158 (1992).

In addition, synthetic oligonucleotides have been used to inhibit a variety of non-viral pathogens, as well as to selectively inhibit the expression of certain cellular genes. Thus, the utility of synthetic oligonucleotides as agents to inhibit virus propagation, propagation of non-viral pathogens and selective expression of cellular genes has been well established. However, there is a need for improved oligonucleotides that have greater efficacy in inhibiting such viruses, pathogens and selective gene expression. Various investigators have attempted to meet this need by preparing and testing oligonucleotides having modifications in their internucleoside linkages. Several investigation have shown that such modified oligonucleotides are more effective than their unmodified counterparts. Sarin et al., Proc. Natl. Acad. Sci. U.S.A. 85: 7448-7451 (1988) teaches that oligodeoxynucleoside methylphosphonates are more active as inhibitors of HIV-1 than conventional oligodeoxynucleotides. Agrawal et al., Proc. Natl. Acad. Sci. U.S.A. 85: 7079-7083 (1988) teaches that oligonucleotide phosphorothioates and certain oligonucleotide phosphoramidates are more effective at inhibiting HIV-1 than conventional oligodeoxynucleotides. Agrawal et al., Proc. Natl. Acad. Sci. U.S.A. 86:7790-7794 (1989) discloses the advantage of oligonucleotide phosphorothioates in inhibiting HIV-1 in early and chronically infected cells.

In addition, chimeric oligonucleotides having more than one type of internucleoside linkage within the oligonucleotide have been developed. Chimeric oligonucleotides contain deoxyribonucleosides only, but have regions containing different internucleoside linkages. Pederson et al., U.S. Pat. No. 5,149,797 (Ser. No. 07/480,269; certain claims allowed on Dec. 24, 1991), the teachings of which are hereby incorporated by reference, discloses chimeric oligonucleotides having an oligonucleotide phosphodiester or oligonucleotide phosphorothioate core sequence flanked by oligonucleotide, methylphosphonates or phosphoramidates. Furdon et al., Nucleic Acids Res. 17: 9193-9204 (1989) discloses chimeric oligonucleotides having regions of oligonucleotide phosphodiesters in addition to either oligonucleotide phosphorothioate or methylphosphonate regions. Quartin et al., Nucleic Acids Res. 17: 7523-7562 (1989) discloses chimeric oligonucleotides having regions of oligonucleotide phosphodiesters and oligonucleotide methylphosphonates. Each of the above compounds contains deoxyribonucleotide phosphorothioates, which have reduced duplex stability. Atabekov et al., FEBS Letters 232:96-98 (1988) discloses chimeric oligonucleotides in which all internucleoside linkages are phosphodiester linkages, but in which regions of ribonucleotides and deoxyribonucleotides are mixed. Inoue et al., FEBS Letters, 215: 237-250 (1987) discloses chimeric oligonucleotides having only phosphodiester linkages, and regions of deoxyribonucleotides and 2'-OMe-ribonucleotides. None of these compounds having solely phosphodiester linkages exhibit either endonuclease or exonuclease resistance.

Many of these modified oligonucleotides have contributed to improving the potential efficacy of the antisense oligonucleotide therapeutic approach. However, certain deficiencies remain in the known oligonucleotides, and these deficiencies can limit the effectiveness of such oligonucleotides as therapeutic agents. Wickstrom, J. Biochem. Biophys. Methods 13: 97-102 (1986) teaches that oligonucleotide phosphodiesters are susceptible to nuclease-mediated degradation. Such nuclease susceptibility can limit the bioavailability of oligonucleotides in vivo. Agrawal et al., Proc. Natl. Acad. Sci. U.S.A. 87: 1401-1405 (1990) teaches that oligonucleotide phosphoramidates or methylphosphonates when hybridized to RNA do not activate RNase H, the activation of which can be important to the function of antisense oligonucleotides. Agrawal et al., Nucleosides & Nucleotides 8: 5-6 (1989) teaches that oligodeoxyribonucleotide phosphorothioates have reduced duplex stability when hybridized to RNA.

There is, therefore, a need for improved oligonucleotides that overcome the deficiencies of oligonucleotides that are known in the art. Ideally, such oligonucleotides should be resistant to nucleolytic degradation, should form stable duplexes with RNA, and should activate RNase H when hybridized with RNA.

BRIEF SUMMARY OF THE INVENTION

The invention provides hybrid oligonucleotides (containing segments of deoxy- and ribo nucleotides) that resist nucleolytic degradation, form stable duplexes with RNA or DNA, and activate RNase H when hybridized with RNA. Oligonucleotides according to the invention provide these features by having phosphorothioate and/or phosphorodithioate internucleoside linkages and segments of oligodeoxyribonucleotides as well as segments of either oligoribonucleotides or 2'-substituted-oligoribonucleotides. For purposes of the invention, the term "2'-substituted" means substitution of the 2'-OH of the ribose molecule with, -O-lower alkyl containing 1-6 carbon atoms, aryl or substituted aryl or allyl having 2-6 carbon atoms e.g., 2'-OMe, 2'-O-allyl, 2'-Oaryl, 2'-O-alkyl, 2'-halo, or 2'-amino, but not with 2'H, wherein allyl, aryl, or alkyl groups may be unsubstituted or substituted, e.g., with halo, hydroxy, trifluoromethyl, cyano, nitro, acyl, acyloxy, alkoxy, carboxyl, carbalkoxyl or amino groups.

An object of the invention is to provide oligonucleotides that can be used to analyze and explain the importance to the effectiveness of antisense oligonucleotides of the parameters of nuclease resistance, duplex stability and RNase H activation. Another object of the invention is to provide oligonucleotides that are effective for regulating cellular, pathogen, or viral gene expression at the mRNA level. Yet another object of the invention is to provide therapeutic oligonucleotides that have great efficacy in the antisense oligonucleotide therapeutic approach. Oligonucleotides according to the invention are useful in satisfying each of these objects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show ion exchange HPLC analysis of nuclease treated oligonuclcotides. In panel A, profiles A, B and C are of oligonuclcotides F, C and A, respectively after 420 minutes SVPD digestion. In panel B, profile A is of an undigested oligonucleotide phosphodiester and profile B is of the same after 1 minute SVPD digestion (SVPD concentration one tenth that in Panel A).

FIG. 2 shows results of RNase H activation studies for oligonuclcotides, as described in Example 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first aspect, the invention provides oligonucleotides that are useful for studying the parameters that are important for effective antisense oligonucleotide action. For purposes of the invention, the term oligonucleotide includes polymers of two or more ribonucleotides, deoxyribonucleotides, or both, with ribonucleotide and/or deoxyribonucleotide monomers being connected together via 5' to 3' linkages which may include any of the linkages that are known in the antisense oligonucleotide art. In addition, the term oligonuclcotides includes such molecules having modified nucleic acid/bases and/or sugars, as well as such molecules having added substituents, such as diamines, cholesteryl or other lipophilic groups. Certain preferred combinations of monomers and inter-monomer linkages are discussed in greater detail below.

It is generally believed that the activity of an antisense oligonucleotide depends on the binding of the oligonucleotide to the target nucleic acid, thus disrupting the function of the target, either by hybridization arrest or by destruction of target RNA by RNase H. These mechanisms of action suggest that two parameters should be important to antisense oligonucleotide activity: duplex stability and RNase H activation. Duplex stability is important, since the oligonucleotide presumably must form a duplex (or triplex in the Hoogsteen pairing mechanism) with the target nucleic acid to act either by hybridization arrest or by RNase H-mediated target destruction. RNase H activation (the ability to activate RNase H when hybridized with target RNA) is implicated when the target nucleic acid is RNA, since such activation can lead to the effective destruction of the target RNA molecule. In addition, for an antisense oligonucleotide to act in vivo, it must survive long enough to interact with the target nucleic acid. Given the fact that the in vivo environment contains endonuclease and exonuclease activities, a third parameter arises from this requirement; namely that the antisense oligonucleotide should resist nucleolytic degradation.

To analyze and explain the importance of each of these parameters to the effectiveness of antisense oligonucleotides, it is necessary to have oligonucleotides that vary in each of these parameters. The properties of several known oligonucleotides are shown in Table I, below.

                  TABLE I     ______________________________________     PROPERTIES OF OLIGONUCLEOTIDES                   Duplex    Nuclease  RNase H     Oligonucleotide                   Stability.sup.1                             Resistance.sup.2                                       Activation.sup.3     ______________________________________     Oligodeoxyribonucleotide                   --        --        Yes     (phosphate)     Oligodeoxyribonucleotide                   Lower     +         Yes     (phosphorothioate)     Oligodeoxyribonucleotide                   Lower     ++        Yes     (phosphorodithioate)     Oligodeoxyribonucleotide                   Lower     +         N.K.     (selenoate)     Oligodeoxyribonucleotide                   Lower     +++       No     (phosphoramidate)     Oligoribonucleotide                   Higher    --        No     (phosphate)     Oligoribonucleotide                   Higher    +         No     (phosphorothioate)     2'-OMe-Oligonucleotide                   Higher    +         No     (phosphate)     2'-OMe-Oligoribonucleotide                   Higher    ++        No     (phosphorothioate)     Oligodeoxyribonucleotide                   Lower     +++       No     (methylphosphonate)     ______________________________________      .sup.1 Duplex stability of oligonucleotide to complementary      oligoribonucleotide under physiological conditions, compared to DNARNA      stability.      .sup.2 Compared to DNA (phosphodiesterase digestion).      .sup.3 Activation of RNase H by the duplex formed between oligonucleotide      and RNA.      N.K.  Not known

Hybrid oligonucleotides according to the invention form more stable duplexes with complementary RNA than oligodeoxyribonucleotide phosphorothioates. In addition, they are more resistant to endonucleolytic and exonucleolytic degradation than oligodeoxyribonucleotide phosphorothioates and they normally activate RNase H. Consequently, oligonucleotides according to the invention complement the oligonucleotides shown in Table I in studies of the parameters involved in the effectiveness of antisense oligonucleotides.

With respect to this first aspect of the invention, oligonucleotides according to the invention can have any oligonucleotide sequence, since complementary oligonucleotides used in such study can be prepared having any oligonucleotide sequence. Oligonucleotides according to this aspect of the invention are characterized only by the following features. First, at least some of the internucleoside linkages present in oligonucleotides according to the invention are phosphorothioate and/or phosphorodithioate linkages. In various embodiments, the number of phosphorothioate and/or phosphorodithioate internucleotide linkages can range from 1 to as many internucleotide linkages as are present in the oligonucleotide. Thus, for purposes of the invention, the term oligonucleotide phosphorothioate and/or phosphorodithioate is intended to encompass every such embodiment. In a preferred embodiment, oligonucleotides according to the invention will range from about 2 to about 50 nucleotides in length, and most preferably from about 6 to about 50 nucleotides in length. Thus, in this preferred embodiment, oligonucleotides according to the invention will have from 1 to about 49 phosphorothioate and/or phosphorodithioate internucleotide linkages.

A second feature of oligonucleotides according to this aspect of the invention is the presence of deoxyribonucleotides. Oligonucleotides according to the invention contain at least one deoxyribonucleotide. Preferably oligonucleotides according to the invention contain four or more deoxyribonucleotides in a contiguous block, so as to provide an activating segment for RNase H. In certain preferred embodiments, more than one such activating segment will be present. Such segments may be present at any location within the oligonucleotide. There may be a majority of deoxyribonucleotides in oligonucleotides according to the invention. In fact, such oligonucleotides may have as many as all but one nucleotide being deoxyribonucleotides. Thus, in a preferred embodiment, having from about 2 to about 50 nucleotides or most preferably from about 6 to about 50 nucleotides, the number of deoxyribonucleotides present will range from 1 to about 49 deoxyribonucleotides.

A third feature of oligonucleotides according to this aspect of the invention is the presence of ribonucleotides, 2'-substituted ribonucleotides or combinations thereof. For purposes of the invention, the term "2'-substituted" means substitution of the 2'-OH of the ribose molecule with, e.g., 2'-OMe, 2'-O-allyl, 2'-O-aryl, 2'-O-alkyl, 2'-halo, or 2'-amino, but not with 2'-H, wherein allyl, aryl, or alkyl groups may be unsubstituted or substituted, e.g., with halo, hydroxy, trifluoromethyl, cyano, nitro, acyl, acyloxy, alkoxy, carboxyl, carbalkoxyl or amino groups. Oligonucleotides according to the invention contain at least one ribonucleotide and/or 2'-substituted ribonucleotide. In a preferred embodiment, such oligonucleotides have 6 or more ribonucleotides and/or 2'-substituted ribonucleotides to enhance duplex stability. Such ribonucleotides and/or 2'-substituted ribonucleotides can be present singly, in pairs, or in larger contiguous segments, and may be present at any position within the oligonucleotide or at multiple positions within the oligonucleotide. Such ribonucleotides and/or 2'-substituted ribonucleotides may comprise as many as all but one nucleoside within the oligonucleotides. Thus, in a preferred embodiment, having from about 2 to about 50 nucleotides or most preferably from about 6 to about 50 nucleotides, the number of ribonucleosides or 2'-substituted ribonucleotides will range from about 1 to about 49 deoxyribonucleotides.

The ability to vary the numbers and positions of phosphorothioate and/or phosphorodithioate internucleotide linkages, deoxyribonucleotides, and ribonucleotides or 2'-substituted ribonucleotides allows the investigator to examine in detail how each of these variables affects the parameters of nuclease resistance, duplex stability and RNase H activation. The ability to vary the size of the oligonucleotide allows examination of yet another parameter. In addition, smaller oligos (e.g., dimers) can be used as building blocks for larger oligos. Thus, the embodiments described above are useful in such studies.

In a second aspect, the invention provides hybrid oligonucleotides that are effective in inhibiting viruses, pathogenic organisms, or the expression of cellular genes. The ability to inhibit such agents is clearly important to the treatment of a variety of disease states. Oligonucleotides according to this aspect of the invention share the characteristics of the above-described oligonucleotides, except that the oligonucleotide sequence of oligonucleotides according to this aspect of the invention is complementary to a nucleic acid sequence that is from a virus, a pathogenic organism or a cellular gene. Preferably such oligonucleotides are from about 6 to about 50 nucleotides in length. For purposes of the invention, the term "oligonucleotide sequence that is complementary to a nucleic acid sequence" is intended to mean an oligonucleotide sequence (2 to about 50 nucleotides) that binds to the nucleic acid sequence under physiological conditions, e.g. by Watson-Crick base pairing (interaction between oligonucleotide and single-stranded nucleic acid) or by Hoogsteen base pairing (interaction between oligonucleotide and double-stranded nucleic acid) or by any other means including in the case of a oligonucleotide binding to RNA, pseudoknot formation. Such binding (by Watson Crick base pairing) under physiological conditions is measured as a practical matter by observing interference with the function of the nucleic acid sequence.

The nucleic acid sequence to which an oligonucleotide according to the invention is complementary will vary, depending upon the agent to be inhibited. In many cases the nucleic acid sequence will be a virus nucleic acid sequence. The use of antisense oligonucleotides to inhibit various viruses is well known, and has recently been reviewed in Agrawal, Trends in Biotech 10: 152-158 (1992). Viral nucleic acid sequences that are complementary to effective antisense oligonucleotides have been described for many viruses, including human immunodeficiency virus type 1 (U.S. Pat. No. 4,806,463, the teachings of which are hereby incorporated by reference), herpes simplex virus (U.S. Pat. No. 4,689,320, the teachings of which are hereby incorporated by reference), influenza virus (U.S. Pat. No. 5,194,428; Ser. No. 07/516,275, certain claims allowed Jun. 30, 1992; the teachings of which are hereby incorporated by reference), and Human papilloma virus (Storey et al., Nucleic Acids Res. 19:4109-4114 (1991)). Sequences complementary to any of these nucleic acid sequences can be used for oligonucleotides according to the invention, as can be oligonucleotide sequences complementary to nucleic acid sequences from any other virus. Additional viruses that have known nucleic acid sequences against which antisense oligonucleotides can be prepared include foot and mouth disease virus (See Robertson et al., J. Virology 54:651 (1985); Harris et al., J. Virology 36:659 (1980)), yellow fever virus (See Rice et al., Science 229:726 (1985)), varicella-zoster virus (See Davison and Scott, J. Gen. Virology 67:2279 (1986), and cucumber mosaic virus (See Richards et al., Virology 89:395 (1978)).

Alternatively, oligonucleotides according to the invention can have an oligonucleotide sequence complementary to a nucleic acid sequence of a pathogenic organism. The nucleic acid sequences of many pathogenic organisms have been described, including the malaria organism, Plasmodium falciparum, and many pathogenic bacteria. Oligonucleotide sequences complementary to nucleic acid sequences from any such pathogenic organism can be used in oligonucleotides according to the invention. Examples of pathogenic eukaryotes having known nucleic acid sequences against which antisense oligonucleotides can be prepared include Trypanosom abraucei gambiense and Leish mania (See Campbell et al., Nature 311:350 (1984)), Fasciola hepatica (See Zurita et al., Proc. Natl. Acad. Sci. U.S.A. 84: 2340 (1987). Antifungal oligonucleotides can be prepared using a target hybridizing region having an oligonucleotide sequence that is complementary to a nucleic acid sequence from, e.g., the chitin synthetase gene, and antibacterial oligonucleotides can be prepared using, e.g., the alanine racemase gene.

In yet another embodiment, the oligonucleotides according to the invention can have an oligonucleotide sequence complementary to a cellular gene or gene transcript, the abnormal expression or product of which results in a disease state. The nucleic acid sequences of several such cellular genes have been described, including prion protein (Stahl and Prusiner, FASEB J. 5:2799-2807 (1991)), the amyloid-like protein associated with Alzheimer's disease (U.S. Pat. No. 5,015,570, the teachings of which are hereby incorporated by reference), and various well-known oncogenes and proto-oncogenes, such as c-myb, c-myc, c-abl, and n-ras. In addition, oligonucleotides that inhibit the synthesis of structural proteins or enzymes involved largely or exclusively in spermatogenesis, sperm motility, the binding of the sperm to the egg or any other step affecting sperm viability may be used as contraceptives. Similarly, contraceptives for women may be oligonucleotides that inhibit proteins or enzymes involved in ovulation, fertilization, implantation or in the biosynthesis of hormones involved in those processes.

Hypertension may be controlled by oligodeoxynucleotides that suppress the synthesis of angiotensin converting enzyme or related enzymes in the renin/angiotensin system; platelet aggregation may be controlled by suppression of the synthesis of enzymes necessary for the synthesis of thromboxane A2 for use in myocardial and cerebral circulatory disorders, infarcts, arteriosclerosis, embolism and thrombosis; deposition of cholesterol in arterial wall may be inhibited by suppression of the synthesis of fatty acid co-enzyme A:cholesterol acyl transferase in arteriosclerosis; inhibition of the synthesis of cholinephosphotransferase may be useful in hypolipidemia.

There are numerous neural disorders in which hybridization arrest may be used to reduce or eliminate adverse effects of the disorder. For example, suppression of the synthesis of monoamine oxidase may be used in Parkinson's disease; suppression of catechol o-methyl transferase may be used to treat depression; and suppression of indole N-methyl transferase may be used in treating schizophrenia.

Suppression of selected enzymes in the arachidonic acid cascade which leads to prostaglandins and leukotrienes may be useful in the control of platelet aggregation, allergy, inflammation, pain and asthma.

Suppression of the protein expressed by the multidrug resistance (mdr) gene, which can be responsible for development of resistance of tumors to a variety of anti-cancer drugs and is a major impediment in chemotherapy may prove to be beneficial in the treatment of cancer. Oligonucleotide sequences complementary to nucleic acid sequences from any of these genes can be used for oligonucleotides according to the invention, as can be oligonucleotide sequences complementary to any other cellular gene or gene transcript, the abnormal expression or product of which results in a disease state.

Antisense regulation of gene expression in plant cells has been described in U.S. Pat. No. 5,107,065, the teachings of which are hereby incorporated by reference.

In a third aspect, the invention provides therapeutic pharmaceutical formulations of oligonucleotides that are effective for treating virus infection, infections by pathogenic organisms, or disease resulting from abnormal gene expression or from the expression of an abnormal gene product. Such therapeutic pharmaceutical formulations comprise the oligonucleotides according to the second aspect of the invention in a pharmaceutically acceptable carrier.

In a fourth aspect, the invention provides a method for inhibiting the gene expression of a virus, a pathogenic organism or a cellular gene, the method comprising the step of providing oligonucleotides according to the invention to cells infected with the virus or pathogenic organism in the former two cases or to cells generally in the latter case. Such methods are useful in studying gene expression and the function of specific genes.

In a fifth aspect, the invention provides a method of treating a diseased human or animal in which the disease results from infection with a virus or pathogenic organism, or from the abnormal expression or product of a cellular gene. The method comprises administering therapeutic pharmaceutical formulations of oligonucleotides according to the invention to the diseased human or animal. Preferably, the routes of such administration will include oral, intranasal, rectal and topical administration. In such methods of treatment according to the invention the oligonucleotides may be administered in conjunction with other therapeutic agents, e.g., AZT in the case of AIDS.

A variety of viral diseases may be treated by the method of treatment according to the invention, including AIDS, ARC, oral or genital herpes, papilloma warts, flu, foot and mouth disease, yellow fever, chicken pox, shingles, adult T cell-leukemia, and hepatitis. Among fungal diseases that may be treatable by the method of treatment according to the invention are candidiasis, histoplasmosis, cryptococcocis, blastomycosis, aspergillosis, sporotrichosis, chromomycosis, dermatophytosis and coccidioidomycosis. The method might also be used to treat rickettsial diseases (e.g., typhus, Rocky Mountain spotted fever), as well as sexually transmitted diseases caused by Chlamydia trachomatis or Lymphogranuloma venereum. A variety of parasitic diseases may be treated by the method according to the invention, including amebiasis, Chegas' disease, toxoplasmosis, pneumocystosis, giardiasis, cryptosporidiosis, trichomoniasis, and Pneumocystis carini pneumonia; also worm (helminthic) diseases such as ascariasis, filariasis, trichinosis, schistosomiasis and nematode or cestode infections. Malaria may be treated by the method of treatment of the invention regardless of whether it is caused by P. falcip arum, P. vivax, P. orale, or P. malariae.

The infectious diseases identified above may all be treated by the method of treatment according to the invention because the infectious agents for these diseases are known and thus oligonucleotides according to the invention can be prepared, having oligonucleotide sequence that is complementary to a nucleic acid sequence that is an essential nucleic acid sequence for the propagation of the infectious agent, such as an essential gene.

Other disease states or conditions that may be treatable by the method according to the invention are those which result from an abnormal expression or product of a cellular gene. These conditions may be treated by administration of oligonucleotides according to the invention, and have been discussed earlier in this disclosure.

Oligonucleotides according to the invention can be synthesized by procedures that are well known in the art. Alternatively, and preferably such oligonucleotides can be synthesized by the H-phosphonate approach described in U.S. Pat. No. 5,149,798 (Ser. No. 07/334,679; allowed on Mar. 10, 1992), the teachings of which are hereby incorporated by reference, and in Agrawal and Tang, Tetrahedron Lett. 31:7541-7544 (1990). Oligonucleotides according to the invention can be made even more resistant to nucleolytic degradation through the addition of cap structures at the 5' and/or 3' end.

The following examples are intended to further illustrate certain preferred embodiments of the invention and are not intended to be limiting in nature.

Example 1 Synthesis of Hybrid Oligonucleotide Phosphorothioates

Hybrid oligonucleotide phosphorothioates were synthesized on CPG on a 5-6 μmole scale on an automated synthesizer (model 8700, Millipore, Milford, Mass.) using the H-phosphonate approach described in U.S. Pat. No. 5,149,798 (Ser. No. 07/334,679; allowed on Mar. 19, 1992). Deoxynucleoside H-phosphonates were obtained from Millipore. 2'-OMe ribonucleotide H-phosphonates were synthesized by standard procedures. Segments of oligonucleotides containing 2'-OMe nucleoside were assembled by using 2'-OMe ribonucleoside H-phosphonates for the desired cycles. Similarly, segments of oligonucleotides containing deoxyribonucleosides were assembled by using deoxynucleoside H-phosphonates for the desired cycles. After assembly, CPG bound oligonucleotide H-phosphonate was oxidized with sulfur to generate the phosphorothioate linkage. Oligonucleotides were then deprotected in concentrated NH₄ OH at 40° C. for 48 hours.

Crude oligonucleotide (about 500 A₂₆₀ units) was analyzed on reverse low pressure chromatography on a C₁₈ reversed phase medium. The DMT group was removed by treatment with 80% aqueous acetic acid, then the oligonucleotides were dialyzed against distilled water and lyophilized.

The oligonucleotides synthesized are shown in Table II, below.

                  TABLE II     ______________________________________     HYBRID OLIGONUCLEOTIDE PHOSPHOROTHIOATES*     SYNTHESIZED     Oligo  Structure     ______________________________________     A      .sup.5' A C A C C C A A T T C T G A A A A T G G.sup.3'     B      A C A C C C A A T T C U G A A A A U G G     C      A C A C C C A A T T C T G A A A A U G G     D      A C A C C C A A T T C U G A A A A U G G     E      A C A C C C A A U T C T G A A A A T G G     F      A C A C C C A A U U C U G A A A A U G G     ______________________________________      Underlined sequences contain 2'-OMe ribonucleoside.      *All internucleoside linkages are phosphorothioate linkages for oligos      A-F.

Example 2 Relative Nuclease Resistance of Hybrid Oligonucleotide Phosphorothioates

To test the relative nuclease resistance of various hybrid oligonucleotide phosphorothioates, the oligonucleotides were treated with snake venom phosphodiesterase (SVPD). About 0.2 A₂₆₀ units of oligos A, C and F were dissolved in 500 μl buffer (40 mM NH₄ CO₃, pH 0.4+20 mM MgCl₂) and mixed with 0.1 units SVPD. The mixture was incubated at 37° C. for 420 minutes. After 0, 200 and 420 minutes, 165 μl aliquots were removed and analyzed using ion exchange HPLC. The results are shown in FIG. 1. Oligonucleotide F was very resistant to phosphodiesterase, whereas oligonucleotide A was digested almost to completion and oligonucleotide C was digested to 50% (panel A). An oligonucleotide phosphodiester was digested to about 80% in one minute using one tenth of the concentration of SVPD. (panel B)

These results indicate that the presence of 2'-OMe ribonucleotides in an oligonucleotide phosphorothioate enhances resistance to exonucleolytic digestion and that this enhanced resistance increases when a larger proportion of 2'-OMe ribonucleotides are used. Due to the similar character and behavior of ribonucleotides, other 2'-substituted ribonucleotides and 2'-OMe ribonucleotides, these results also suggest that similar enhancement of nuclease resistance would be obtained for hybrid oligonucleotide phosphorothioates and/or phosphorodithioates having ribonucleotides, 2'-substituted ribonucleotides, or a mixture of ribonucleotides and 2'-substituted ribonucleotides.

Example 3 Relative Duplex Stability of Hybrid Oligonucleotide Phosphorothioates

Oligonucleotides A-F were tested for the relative stability of duplexes formed between them and complementary oligodeoxyribonucleotides, and with complementary oligoribonucleotides. In separate reactions, each oligonucleotide a-F was mixed with an equivalent quantity (0.2 A₂₆₀ units) of its complementary oligonucleotide in 150 mM NaCl, 10 mM Na₂ PO₄, 1 mM EDTA, pH 7. The mixture was heated to 85° C. for 5 minutes, then cooled to 30° C. The temperature was then increased from 30° C. to 80° C. at a rate of 1° C. per minute and A₂₆₀ was recorded as a function of temperature. The results are shown in Table III, below.

                                      TABLE III     __________________________________________________________________________     MELTING TEMPERATURE OF DUPLEXES                                            DNA-RNA Duplex            DNA-DNA Duplex                        DNA-RNA Duplex      w/Magnesium                 Difference in                             Difference in       Difference in                 Tm compared Tm compared         Tm                 to          to     Tm DNA-RNA   compared to            Tm DNA                 oligonucleo-                        Tm RNA                             oligonucleo-                                    Duplex-Tm DNA                                            Tm RNA                                                 oligonucleo-     Oligonucletide            (°C.)                 tide A (°C.)                        (°C.)                             tide A (°C.)                                    Duplex (°C.)                                            (°C.)                                                 tide A (°C.)     __________________________________________________________________________     A      51.1 0      43.4 0      -7.7    48.1 0     B      48.3 -2.8   50.9 7.5    2.6     58.4 10.3     C      49.9 -1.2   48.9 5.5    -1.0    54.2 6.1     D      45.1 -6.0   50.9 7.5    5.8     56.1 8.0     E      47.2 -3.9   51.1 7.7    3.9     56.5 8.4     F      47.6 -3.5   61.1 17.7   13.5    69.1 21.0     __________________________________________________________________________

These results reveal that when the complementary oligonucleotide is an oligoribonucleotide, the presence of 2'-OMe ribonucleotides enhances duplex stability, and that this enhancement increases with increased proportions of 2'-OMe ribonucleotides. These results should be similarly applicable to hybrid oligonucleotide phosphorothioates and/or phosphorodithioates containing ribonucleotides, 2'-substituted ribonucleotides, or mixtures of ribonucleotides and 2'-substituted ribonucleotides. Thus, the hybrid oligonucleotide phosphorothioates and/or phosphorodithioates according to the invention should bind viral RNA or virus, pathogenic organism or cellular mRNA with greater affinity than ordinary oligodeoxynucleotide phosphorothioates.

Example 4 Activation of RNase H by Hybrid Oligonucleotide Phosphorothioates

Oligonucleotide phosphorothioates and various hybrid oligonucleotide phosphorothioates were studied for their RNase H activation properties. Oligonucleotide A (Table II), an oligonucleotide phosphorothioate which is known to activate RNase H, was used as a control. Oligonucleotide F (a 2'-OMe analog of oligonucleotide phosphorothioate) and oligonucleotides C, B, and E, hybrid oligonucleotides, were studied for their ability to activate RNase H.

To carry out the experiment, a complementary 32-mer oligoribonucleotide was synthesized (FIG. 2) and kinased at the 5'-end, ³² P-labeled 32-mer RNA (0.003 A₂₆₀ units; 0.01 μg) and oligonucleotides (0.0635 A₂₆₀ units; 1.9 μg) were mixed in the 20 μl of buffer (0.15M NaCl, 0.01 MgCl₂, 0.01M Tris-HCl, pH 7.9, containing 0.001M DTT. The mixture was incubated with 6 units of RNase H (E. coli) at 37° C. Aliquots of 4.5 μl were removed at 0, 15, 30, and 60 minutes and analyzed on polyacrylamide gel electrophoresis.

Oligonucleotide A (duplex A in FIG. 2) showed site specific cleavage of RNA by RNase H. Oligonucleotide F (2'-OMe analog; Duplex 2) showed no cleavage of RNA in presence of RNase H. Hybrid oligonucleotide B, C, B and E (Duplexes 3, 4, 5, resp.) showed site specific cleavage of RNA by RNase H. Duplex 6, in which a mismatched oligonucleotide phosphorothioate was studied showed no cleavage of RNA. Lane (-) shows that in presence of RNase H, RNA was not cleaved.

Example 5 Inhibition of HIV by Hybrid Oligonucleotide Phosphorothioates

Hybrid oligonucleotide phosphorothioates were tested for their ability to inhibit HIV-1 in tissue culture. H9 lymphocytes were infected with HIV-1 virions (=0.01-0.1 TCID₅₀ /cell) for one hour at 37° C. After one hour, unadsorbed virions were washed and the infected cells were divided among wells of 24 well plates. To the infected cells, an appropriate concentration (from stock solution) of oligonucleotide was added to obtain the required concentration in 2 ml medium. The cells were then cultured for four days. At the end of four days, level of HIV-1 expression was measured by synthetic formation, p. 24 expression and reverse transcriptase activity. The level of expression of -24 was compared between oligonucleotide treated and untreated (no drug) infected cells. (Table IV)

All of the hybrid oligonucleotide phosphorothioates tested showed significant inhibition of syncylia formation, p24 expression and reverse transcriptase, without significant cytotoxicity. These results indicate that hybrid oligonucleotide phosphorothioates containing 2'-OMe ribonucleotides are more effective as inhibitors of gene expression compared to oligonucleotide phosphorthioates. Similar effectiveness would be expected for hybrid oligonucleotide phosphorothioates and/or phosphorodithioates containing ribonucleosides, 2'-substituted ribonucleosides, or a mixture of ribonucleosides and 2'-substituted ribonucleosides. The activity of compounds listed in Table III are listed in Table IV below.

                  TABLE IV     ______________________________________     Anti-HIV activity of oligonucleotides (listed in Table III)                                    Inhibition of                           Inhibition                                    Reverse Transcriptase     Oligonucleotides               Syncytia formed                           of p24 (%)                                    (%)     ______________________________________     Oligo A   ++          93       88     Oligo B   ++          95       97     Oligo C   +           98       97     Oligo D   +           98       83     Oligo E   +++         90       94     Oligo F   +++         88       91     + Control ++++     - Control -     ______________________________________      + Control = HIV1 Infected cells without oligonucleotides      - Control = Uninfected cells without oligonucleotides      1. Number of Syncytia formed in oligonucleotide treated cells were      compared with the number of syncytia formed in untreated infected cells.      2. Inhibition is compared to untreated infected cells.

    __________________________________________________________________________     SEQUENCE LISTING     (1) GENERAL INFORMATION:     (iii) NUMBER OF SEQUENCES: 8     (2) INFORMATION FOR SEQ ID NO:1:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     ACACCCAATTCTGAAAATGG20     (2) INFORMATION FOR SEQ ID NO:2:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     ACACCCAATTCUGAAAAUGG20     (2) INFORMATION FOR SEQ ID NO:3:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     ACACCCAATTCTGAAAAUGG20     (2) INFORMATION FOR SEQ ID NO:4:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     ACACCCAATTCUGAAAAUGG20     (2) INFORMATION FOR SEQ ID NO:5:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:     ACACCCAAUTCTGAAAATGG20     (2) INFORMATION FOR SEQ ID NO:6:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:     ACACCCAAUUCUGAAAAUGG20     (2) INFORMATION FOR SEQ ID NO:7:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 20 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:     ACAGACTTACCTCAGATAAT20     (2) INFORMATION FOR SEQ ID NO:8:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 32 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: other nucleic acid     (iii) HYPOTHETICAL: NO     (iv) ANTI-SENSE: YES     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:     UACAGCUGUGGGUUAAGACUUUUACCUAUUUG32     __________________________________________________________________________ 

We claim:
 1. A hybrid oligonucleotide that is complementary to a target RNA, the hybrid oligonucleotide consisting of phosphorothioate nucleotides and comprising a segment of at least two contiguous 2'-O-methyl-substituted ribonucleotides as the terminal two nucleotides at each end of the oligonucleotide, and further comprising a segment of at least three contiguous deoxyribonucleotides.
 2. A hybrid oligonucleotide according to claim 1, wherein the deoxyribonucleotide is present in a segment of at least four contiguous deoxyribonucleotides.
 3. An oligonucleotide according to claim 1 comprising from about 6 to about 50 nucleotides.
 4. An oligonucleotide according to claim 2 comprising from about 6 to about 50 nucleotides.
 5. An oligonucleotide according to claim 1 wherein the target RNA is a RNA from a virus.
 6. An oligonucleotide according to claim 2 wherein the target RNA is a RNA from a virus.
 7. An oligonucleotide according to claim 3 wherein the target RNA is a RNA from a virus.
 8. An oligonucleotide according to claim 4 wherein the target RNA is a RNA from a virus.
 9. An oligonucleotide according to claim 1 wherein the target RNA is a RNA from HIV.
 10. An oligonucleotide according to claim 2 wherein the target RNA is a RNA from HIV.
 11. An oligonucleotide according to claim 3 wherein the target RNA is a RNA from HIV.
 12. An oligonucleotide according to claim 4 wherein the target RNA is a RNA from HIV. 